Many larger electronic systems are contained in one or more cabinets or chassis that allow removal of racks, drawers, or boards. Boards may need to be added or removed while the system is still operating for repair or expansion purposes. In older systems, boards were interconnected by many cables, often creating a confusing nest of cabling.
More recently, a larger board known as a backplane is provided with connector sockets that receive the edges of boards. A midplane is a variation of a backplane that is not located in the back of the chassis, but is located in the middle of the chassis. Connector sockets may be mounted to both sides of a midplane board, allowing boards to be inserted on both surfaces of the midplane.
Boards are inserted perpendicularly to the main surfaces of backplanes and midplanes. Cooling airflow is often directed between the removable boards. Since the backplane or midplane is orthogonal to the removable boards, backplanes and midplanes often act as a wall to block the airflow and to restrict the airflow to a single vertical direction. Holes or notches may be added to the backplane or midplane to allow for some air to flow through, but this may waste valuable component space. Cascading several boards together may require a higher or cooler airflow.
A variety of other configurations have been attempted, such as co-planar backplanes that are mated through a connector, and orthogonal backplanes that mate through specialized connectors. Although co-planner backplanes are parallel to each other, they only span one dimension each and are rarely used. Orthogonal backplanes often require staggering boards and other specialized connectors. The density of the removable boards is often less than desired.
What is desired is an improved high-density interconnect.